Androgen receptor is a critical molecule involved in the normal development of prostate tissues and in the growth and progression of prostate cancer. Mutations of androgen receptor are associated with androgen insensitivity and testicular feminization syndrome as well as prostate cancer. Characterization of these mutations have contributed greatly to our knowledge about the structure-function relationship of androgen receptor, as well as their roles of in development, differentiation and growth of prostate cells. Androgen receptor is a ligand induced transcriptional factor which in combination with co-regulators induce differentiation and growth genes in different cellular context. Androgen receptor activity is modulated not only by its natural ligand, androgen, but also by growth factors and cytokines such as IL-6, EGF and gastrin-releasing peptide. These non-steroid ligands activate tyrosine kinases (e.g., EGF-R and Src) and serine kinases (e.g., MARK and casein kinase), resulting in the post translational modification of androgen receptor including phosphorylation, sumoylation, acetylation and cleavage by proteases. The most troubling aspect of prostate cancer is its conversion to androgen independence, which defies any effective treatment including androgen-ablation. Accumulating evidence suggests that inappropriate activation of androgen receptor by non-steroids and genetic mutation of androgen receptor may represent two major complementary mechanisms responsible for the evolution of androgen independence of prostate cancers. Our lab has been studying both mechanisms and discovered a novel mutation of androgen receptor in CWR22 xenograft, during its evolution to androgen independence. CWR22 xenograft has been used by many laboratories world-wide and become one of the favorite models to study androgen independence conversion. Using a novel allele-replacement approach, we wish to demonstrate that the mutation which duplicates exon 3 of androgen receptor locus is the genetic basis of hormone refractory transformation of this xenograft cell line and uncover a novel new mechanism of androgen independence. This mutation sensitizes androgen receptor toward cleavage by cellular protease calpain and generates a constitutively active receptor carrying only the N-terminal domain. Overexpression of calpain and the cleaved N-terminal domain product are often found in prostate cancer tissues. Signals that modulate calpain activity such as Src tyrosine kinase may contribute to such cleavage in an epigenetic manner. Our proposal will contribute to 1) a detailed understanding of an androgen receptor mutation which underlies androgen independence in CWR22.2) the molecular pathway which contributes to the generation of truncated androgen receptor and 3) the development of an effective allele replacement strategy to study the tumor-associated androgen receptor mutation. The result will provide insights into the genetic and epigenetic mechanisms of androgen independence, which goes beyond the study of CWR22.